Therapeutic considerations of PARP in stem cell biology: Relevance in cancer and beyond

Navigating the therapeutic landscape for breast cancer: targeting breast cancer stem cells

Breast cancer is a common and deadly malignancy that affects women globally, and breast cancer stem cells (BCSCs) play an important role in tumorigenesis, development, metastasis, and recurrence. Traditional therapies often fail to eliminate BCSCs, leading to treatment resistance and relapse. This review explores the therapeutic strategies which are designed to target BCSCs, including inhibition of key signaling pathway and targeting receptor. This paper also explores the approaches to targeting BCSCs including chemotherapy, phytomedicines, and nanotechnology. Nanotechnology has gained a lot of importance in cancer therapy because of its ability to deliver therapeutic agents with more precision and minimal side effects. Various chemotherapeutic drugs, siRNAs, or gene editing tools are delivered efficiently with the use of nanocarriers which target pathways, receptors, and proteins associated with BCSCs. Over the past few years, stimuli-responsive and receptor-targeted nanocarriers have been explored for better therapeutic effects. In recent times, strategies such as chimeric antigen receptor (CAR) T-cell therapy, ablation therapy, and cell-free therapies are explored for targeting these stem cells. This review provides a recent developmental overview of strategies to attack BCSCs from conventional chemotherapeutic agents to nanotechnological platforms such as polymeric, lipidic, and metal-based nanoparticles and advanced technologies like CAR T cell therapies.

Acetylation and deacetylation of histone in adipocyte differentiation and the potential significance in cancer

Adipocytes are derived from pluripotent mesenchymal stem cells and can develop into several cell types including adipocytes, myocytes, chondrocytes, and osteocytes. Adipocyte differentiation is regulated by a variety of transcription factors and signaling pathways. Various epigenetic factors, particularly histone modifications, play key roles in adipocyte differentiation and have indispensable functions in altering chromatin conformation. Histone acetylases and deacetylases participate in the regulation of protein acetylation, mediate transcriptional and post-translational modifications, and directly acetylate or deacetylate various transcription factors and regulatory proteins. The adipocyte differentiation of stem cells plays a key role in various metabolic diseases. Cancer stem cells(CSCs) play an important function in cancer metastasis, recurrence, and drug resistance, and have the characteristics of stem cells. They are expressed in various cell lineages, including adipocytes. Recent studies have shown that cancer stem cells that undergo epithelial-mesenchymal transformation can undergo adipocytic differentiation, thereby reducing the degree of malignancy. This opens up new possibilities for cancer treatment. This review summarizes the regulation of acetylation during adipocyte differentiation, involving the functions of histone acetylating and deacetylating enzymes as well as non-histone acetylation modifications. Mechanistic studies on adipogenesis and acetylation during the differentiation of cancer cells into a benign cell phenotype may help identify new targets for cancer treatment.

Deciphering Common Traits of Breast and Ovarian Cancer Stem Cells and Possible Therapeutic Approaches

Breast cancer (BC) and ovarian cancer (OC) are among the most common and deadly cancers affecting women worldwide. Both are complex diseases with marked heterogeneity. Despite the induction of screening programs that increase the frequency of earlier diagnosis of BC, at a stage when the cancer is more likely to respond to therapy, which does not exist for OC, more than 50% of both cancers are diagnosed at an advanced stage. Initial therapy can put the cancer into remission. However, recurrences occur frequently in both BC and OC, which are highly cancer-subtype dependent. Therapy resistance is mainly attributed to a rare subpopulation of cells, named cancer stem cells (CSC) or tumor-initiating cells, as they are capable of self-renewal, tumor initiation, and regrowth of tumor bulk. In this review, we will discuss the distinctive markers and signaling pathways that characterize CSC, their interactions with the tumor microenvironment, and the strategies they employ to evade immune surveillance. Our focus will be on identifying the common features of breast cancer stem cells (BCSC) and ovarian cancer stem cells (OCSC) and suggesting potential therapeutic approaches.

NAD+-Consuming Enzymes in Stem Cell Homeostasis

Nicotinamide adenine dinucleotide (NAD⁺) is a coenzyme used in redox reactions, energy metabolism, and mitochondrial biogenesis. NAD⁺ is also required as a cofactor by nonredox NAD⁺-dependent enzymes. Hundreds of enzymes that consume NAD⁺ have been identified. The NAD⁺-consuming enzymes are involved in a variety of cellular processes such as signal transduction, DNA repair, cellular senescence, and stem cell (SC) homeostasis. In this review, we discussed how different types of NAD⁺-consuming enzymes regulate SC functions and summarized current research on the roles of the NAD⁺ consumers in SC homeostasis. We hope to provide a more global and integrative insight to the mechanism and intervention of SC homeostasis via the regulation of the NAD⁺-consuming enzymes.

Targeting cancer stem cells in the tumor microenvironment: An emerging role of PARP inhibitors

Cancer stem cells (CSCs) constitute a small population of cancer cells in the tumor microenvironment (TME), which are responsible for metastasis, angiogenesis, drug resistance, and cancer relapse. Understanding the key signatures and resistance mechanisms of CSCs may help in the development of novel chemotherapeutic strategies to specifically target CSCs in the TME. PARP inhibitors (PARPi) are known to enhance the chemosensitivity of cancer cells to other chemotherapeutic agents by inhibiting the DNA repair pathways and chromatin modulation. But their effects on CSCs are still unknown. Few studies have reported that PARPi can stall replication fork progression in CSCs. PARPi also have the potential to overcome chemoresistance in CSCs and anti-angiogenic potentiality as well. Previous reports have suggested that epigenetic drugs can synergistically ameliorate the anti-cancer activities of PARPi through epigenetic modulations. In this review, we have systematically discussed the effects of PARPi on different DNA repair pathways with respect to CSCs and also how CSCs can be targeted either as monotherapy or as a part of combination therapy. We have also talked about how PARPi can help in reversal of chemoresistance of CSCs and the role of PARPi in epigenetic modifications to hinder cancer progression. We have also elaborated on the aspects of research that need to be investigated for development of successful therapeutic interventions using PARPi to specifically target CSCs in the TME.

Difluoromethylornithine (DFMO) Enhances the Cytotoxicity of PARP Inhibition in Ovarian Cancer Cells

Ovarian cancer accounts for 3% of the total cancers in women, yet it is the fifth leading cause of cancer deaths among women. The BRCA1/2 germline and somatic mutations confer a deficiency of the homologous recombination (HR) repair pathway. Inhibitors of poly (ADP-ribose) polymerase (PARP), another important component of DNA damage repair, are somewhat effective in BRCA1/2 mutant tumors. However, ovarian cancers often reacquire functional BRCA and develop resistance to PARP inhibitors. Polyamines have been reported to facilitate the DNA damage repair functions of PARP. Given the elevated levels of polyamines in tumors, we hypothesized that treatment with the polyamine synthesis inhibitor, α-difluoromethylornithine (DFMO), may enhance ovarian tumor sensitivity to the PARP inhibitor, rucaparib. In HR-competent ovarian cancer cell lines with varying sensitivities to rucaparib, we show that co-treatment with DFMO increases the sensitivity of ovarian cancer cells to rucaparib. Immunofluorescence assays demonstrated that, in the presence of hydrogen peroxide-induced DNA damage, DFMO strongly inhibits PARylation, increases DNA damage accumulation, and reduces cell viability in both HR-competent and deficient cell lines. In vitro viability assays show that DFMO and rucaparib cotreatment significantly enhances the cytotoxicity of the chemotherapeutic agent, cisplatin. These results suggest that DFMO may be a useful adjunct chemotherapeutic to improve the anti-tumor efficacy of PARP inhibitors in treating ovarian cancer.

Celastrol and Resveratrol Modulate SIRT Genes Expression and Exert Anticancer Activity in Colon Cancer Cells and Cancer Stem-like Cells

Simple Summary

The recovery rate in patients with metastatic colorectal cancer (CRC) remains low and declines with successive lines of treatment. This phenomenon is caused by the development of drug resistance and the presence of colorectal cancer stem cells (CSCs). Phytochemicals, like -celastrol and resveratrol, are very promising for colon cancer therapy, owing to their low or no toxicity and their pleiotropic activity, enabling them to interact with various biological targets. In the present study, the potential anticancer mechanisms of both compounds against metastatic colon cancer cells and the capacity to eradicate CSCs were investigated.

Abstract

Metastatic colorectal cancer (CRC) remains a hard-to-cure neoplasm worldwide. Its curability declines with successive lines of treatment due to the development of various cancer resistance mechanisms and the presence of colorectal cancer stem cells (CSCs). Celastrol and resveratrol are very promising phytochemicals for colon cancer therapy, owing to their pleiotropic activity that enables them to interact with various biological targets. In the present study, the anticancer activities of both compounds were investigated in metastatic colon cancer cells (LoVo cells) and cancer stem-like cells (LoVo/DX). We showed that celastrol is a very potent anti-tumor compound against metastatic colon cancer, capable of attenuating CSC-like cells at the molecular and cellular levels. In contrast, resveratrol has a much greater effect on colon cancer cells that are expressing standard sensitivity to anticancer drugs, than on CSC-like cells. In addition, both polyphenols have different influences on the expression of SIRT genes, which seems to be at least partly related to their anti-tumor activity.

Poly (ADP-ribose) polymerase (PARP) inhibition in cancer: Potential impact in cancer stem cells and therapeutic implications

Inhibitors of poly(ADP-ribose) polymerase (PARP) are used in mono- or combination therapies for several malignancies. They are also used as maintenance therapy for some cancers after initial treatment. While the focus of this therapeutic approach is on the effect of PARP inhibition on the bulk tumour cells, in this review, we discuss their effect on the cancer stem cells. We identify key mediators and pathways in cancer stem cells whose response to PARP inhibition is not necessarily the same as the rest of the tumour cells. Since the cancer stem cells are known drivers of growth of tumours and their resistance to therapy, the clinical outcome might be drastically different than what is expected, if the effect of PARP inhibition on the cancer stem cells is not taken into account.

PARP5B is required for nonhomologous end joining during tumorigenesis in vivo

Poly(ADP-ribose) polymerases (PARP) act as DNA damage sensors that produce poly(ADP-ribose) (PAR) chains at double-strand breaks, facilitating the recruitment of repair factors. Cancers with homologous recombination defects are sensitive to small molecule PARP inhibitors. Despite PARP5B gene copy number changes in many cancers, the effects of this genetic alteration on tumor phenotype are largely unknown. To better understand this clinical finding, we characterized a PARP5B null mutation in a carcinogen-induced in vivo head and neck squamous cell carcinoma (SCC) model. Reduced PARP5B expression inhibited tumor growth, induced primary tumor differentiation and apoptosis, and inhibited cell proliferation and metastasis. Loss of PARP5B expression-induced ataxia telangiectasia and Rad3 related (ATR) activation and depleted the cancer stem cell fraction. PARP5B null tumor cells lacked 53BP1+ double-strand break foci, ATM activation, and p53 induction compared to PARP5B+/+ cancers. PARP5B null SCC expresses a multiprotein complex containing PML, pRPA, Rad50, Rad51, XRCC1, proliferating cell nuclear antigen (PCNA), and Mcm2, suggesting an HR-mediated repair mechanism at DNA replication foci. Low doses of etoposide combined with the PARP5B inhibitor XAV939 induced senescence and apoptosis in human SCC lines. NBS1 overexpression in these cells inhibited the effects of low-dose etoposide/XAV939 treatment. Our results indicate that PARP5B inhibition is new targeted cancer therapy.

Investigation of the efficacy of paclitaxel on some miRNAs profiles in breast cancer stem cells

Understanding of the functions of microRNAs in breast cancer and breast cancer stem cells have been a hope for the development of new molecular targeted therapies. Here, it is aimed to investigate the differences in the expression levels of let-7a, miR-10b, miR-21, miR-125b, miR-145, miR-155, miR-200c, miR-221, miR-222 and miR-335, which associated with gene and proteins in MCF-7 (parental) and MCF-7s (Mammosphere/stem cell-enriched population/CD44+/CD24-cells) cells treated with paclitaxel. MCF-7s were obtained from parental MCF-7 cells. Cytotoxic activity of paclitaxel was determined by ATP assay. Total RNA isolation and cDNA conversion were performed from the samples. Changes in expression levels of miRNAs were examined by RT-qPCR. Identified target genes and proteins of miRNAs were analyzed with RT-qPCR and western blot analysis, respectively. miR-125b was significantly expressed (2.0946-fold; p = 0.021) in MCF-7s cells compared to control after treatment with paclitaxel. Downregulation of SMO, STAT3, NANOG, OCT4, SOX2, ERBB2 and ERBB3 and upregulation of TP53 genes were significant after 48 h treatment in MCF-7s cells. Protein expressions of SOX2, OCT4, SMAD4, SOX2 and OCT4 also decreased. Paclitaxel induces miR-125b expression in MCF-7s cells. Upregulation of miR-125b may be used as a biomarker for the prediction of response to paclitaxel treatment in breast cancer.

Direct Conversion of Human Fibroblasts into Adipocytes Using a Novel Small Molecular Compound: Implications for Regenerative Therapy for Adipose Tissue Defects

There is a need in plastic surgery to prepare autologous adipocytes that can be transplanted in patients to reconstruct soft tissue defects caused by tumor resection, including breast cancer, and by trauma and other diseases. Direct conversion of somatic cells into adipocytes may allow sufficient functional adipocytes to be obtained for use in regeneration therapy. Chemical libraries of 10,800 molecules were screened for the ability to induce lipid accumulation in human dermal fibroblasts (HDFs) in culture. Chemical compound-mediated directly converted adipocytes (CCCAs) were characterized by lipid staining, immunostaining, and qRT-PCR, and were also tested for adipokine secretion and glucose uptake. CCCAs were also implanted into mice to examine their distribution in vivo. STK287794 was identified as a small molecule that induced the accumulation of lipid droplets in HDFs. CCCAs expressed adipocyte-related genes, secreted adiponectin and leptin, and abundantly incorporated glucose. After implantation in mice, CCCAs resided in granulation tissue and remained adipose-like. HDFs were successfully converted into adipocytes by adding a single chemical compound, STK287794. C/EBPα and PPARγ were upregulated in STK287794-treated cells, which strongly suggests involvement of these adipocyte-related transcription factors in the chemical direct conversion. Our method may be useful for the preparation of autogenous adipocytes for transplantation therapy for soft tissue defects and fat tissue atrophy.

5-Fluorouracil (5-FU) resistance and the new strategy to enhance the sensitivity against cancer: Implication of DNA repair inhibition

5-Fluorouracil (5-FU) has been an important anti-cancer drug to date. With an increase in the knowledge of its mechanism of action, various treatment modalities have been developed over the past few decades to increase its anti-cancer activity. But drug resistance has greatly affected the clinical use of 5-FU. Overcoming this chemoresistance is a challenge due to the presence of cancer stem cells like cells, cancer recurrence, metastasis, and angiogenesis. In this review, we have systematically discussed the mechanism of 5-FU resistance and advent strategies to increase the sensitivity of 5-FU therapy including resistance reversal. Special emphasis has been given to the cancer stem cells (CSCs) mediated 5-FU chemoresistance and its reversal process by different approaches including the DNA repair inhibition process.

Bioinformatics Analysis Reveals an Association Between Cancer Cell Stemness, Gene Mutations, and the Immune Microenvironment in Stomach Adenocarcinoma

Cancer stem cells (CSCs), characterized by infinite proliferation and self-renewal, greatly challenge tumor therapy. Research into their plasticity, dynamic instability, and immune microenvironment interactions may help overcome this obstacle. Data on the stemness indices (mRNAsi), gene mutations, copy number variations (CNV), tumor mutation burden (TMB), and corresponding clinical characteristics were obtained from The Cancer Genome Atlas (TCGA) and UCSC Xena Browser. The infiltrating immune cells in stomach adenocarcinoma (STAD) tissues were predicted using the CIBERSORT method. Differentially expressed genes (DEGs) between the normal and tumor tissues were used to construct prognostic models with weighted gene co-expression network analysis (WGCNA) and Lasso regression. The association between cancer stemness, gene mutations, and immune responses was evaluated in STAD. A total of 6,739 DEGs were identified between the normal and tumor tissues. DEGs in the brown (containing 19 genes) and blue (containing 209 genes) co-expression modules were used to perform survival analysis based on Cox regression. A nine-gene signature prognostic model (ARHGEF38-IT1, CCDC15, CPZ, DNASE1L2, NUDT10, PASK, PLCL1, PRR5-ARHGAP8, and SYCE2) was constructed from 178 survival-related DEGs that were significantly related to overall survival, clinical characteristics, tumor microenvironment immune cells, TMB, and cancer-related pathways in STAD. Gene correlation was significant across the prognostic model, CNVs, and drug sensitivity. Our findings provide a prognostic model and highlight potential mechanisms and associated factors (immune microenvironment and mutation status) useful for targeting CSCs.

Signaling pathways and microRNAs, the orchestrators of NANOG activity during cancer induction

Cancer stem cells (CSCs) are a small part of cancer cells inside the tumor that have similar characteristics to normal stem cells. CSCs stimulate tumor initiation and progression in a variety of cancers. Several transcription factors such as NANOG, SOX2, and OCT4 maintain the characteristics of CSCs and their upregulation is seen in many malignancies resulting in increased metastasis, invasion, and recurrence. Among these factors, NANOG plays an important role in regulating the self-renewal and pluripotency of CSCs and the clinical significance of NANOG has been suggested as a marker of CSCs in many cancers. The up and down-regulation of NANOG is associated with several important signaling pathways, including JAK/STAT, Wnt/β-catenin, Notch, TGF-β, Hedgehog, and several microRNAs (miRNAs). In this review, we will investigate the function of NANOG in CSCs and the molecular mechanism of its regulation by signaling pathways and miRNAs. We will also investigate targeting NANOG with different techniques, which is a promising treatment strategy for cancer treatment.

Molecular Mechanism of Stem Cell Differentiation into Adipocytes and Adipocyte Differentiation of Malignant Tumor

Adipogenesis is the process through which preadipocytes differentiate into adipocytes. During this process, the preadipocytes cease to proliferate, begin to accumulate lipid droplets, and develop morphologic and biochemical characteristics of mature adipocytes. Mesenchymal stem cells (MSCs) are a type of adult stem cells known for their high plasticity and capacity to generate mesodermal and nonmesodermal tissues. Many mature cell types can be generated from MSCs, including adipocyte, osteocyte, and chondrocyte. The differentiation of stem cells into multiple mature phenotypes is at the basis for tissue regeneration and repair. Cancer stem cells (CSCs) play a very important role in tumor development and have the potential to differentiate into multiple cell lineages. Accumulating evidence has shown that cancer cells can be induced to differentiate into various benign cells, such as adipocytes, fibrocytes, osteoblast, by a variety of small molecular compounds, which may provide new strategies for cancer treatment. Recent studies have reported that tumor cells undergoing epithelial-to-mesenchymal transition can be induced to differentiate into adipocytes. In this review, molecular mechanisms, signal pathways, and the roles of various biological processes in adipose differentiation are summarized. Understanding the molecular mechanism of adipogenesis and adipose differentiation of cancer cells may contribute to cancer treatments that involve inducing differentiation into benign cells.